On the ingredient form, in the Allergens / Dislikes section, pick values in the Allergens and Dislikes multi-selects and save; you can also edit them inline from the list. Customers can set their own allergens and dislikes on their profile (when Theme: Kitchen > Show Allergens / Show Dislikes are set to Yes). Sprwt then checks meals against the profile: the built-in tip explains that meals containing a matching allergen or dislike are blocked/flagged for that customer. Theme: Kitchen > Allergen Badge Visibility in Order Modules controls whether allergen badges show always or only when the customer has allergens on their profile, and Business: Cart > Show meal alergens/dislikes in checkout invoice adds them to invoices.